The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a recyclable retaining ring used on a carrier head in a chemical mechanical polishing system.
Many different manufacturing operations use chemical mechanical polishing; one such operation is the manufacturing of integrated circuits. Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly more non-planar. This occurs because the distance between the outer surface and the underlying substrate is greatest in regions of the substrate where the least etching has occurred, and the distance is least in regions where the greatest etching has occurred. With a single patterned underlying layer, this non-planar surface comprises a series of peaks and valleys where the distance between the highest peak and the lowest valley may be on the order of 5,000 to 12,000 Angstroms. With multiple patterned underlying layers, the height difference between the peaks and the valleys becomes even more severe and can reach several microns.
This non-planar outer surface presents a problem for integrated circuit manufacturers. If the outer surface is non-planar, then photolithographic techniques to pattern photoresist layers might not be suitable, as a non-planar surface can prevent proper focusing of the photolithography apparatus. Therefore, there is a need to periodically planarize this substrate surface. Planarization, in effect, polishes away peaks and valleys of non-planar outer surface layers of the integrated circuit, whether conductive, semiconductive, or insulative layers, to form a relatively flat smooth surface. Following planarization, additional layers may be deposited on the outer layer to form interconnect lines between features, or the outer layer may be etched to form vias to lower features.
Chemical mechanical polishing, commonly referred to as CMP, is a method of planarizing or polishing substrates. In a typical CMP process, a rotating polishing pad, which receives a chemically reactive slurry is used to polish the outermost surface and layers of the substrate. The substrate is positioned over the polishing pad, which is typically mounted in a carrier and retaining ring assembly. The carrier and retaining ring assembly maintains a bias force between the surface of the substrate and the rotating polishing pad. The movement of the slurry-whetted polishing pad across the surface face of the substrate causes material to be chemically and mechanically polished (removed) from that face of the substrate.
Different types of pads and slurry mixtures may be used. Each polishing pad provides a polishing surface which, in combination with the particular slurry mixture, can provide specific polishing characteristics. Thus, for any material being polished, the pad and slurry combination is selected to provide a desired finish and flatness on the polished surface. The pad and slurry combination can provide this finish and flatness in a predetermined polishing time. Additional factors, such as the relative speed between the substrate and the pad, and the force pressing the substrate against the pad affect the polishing rate finish and flatness.
One problem with conventional CMP processing is the high volume of wearable parts which are consumed as the substrates are polished. Generally, a retaining ring assembly is mounted under a substrate carrier that continually wears down as the polishing pad makes direct contact against featured substrate layer surfaces. Consequently, the retaining ring assembly burdens a significant cost as a consumable item for general CMP systems because the entire assembly needs to be discarded and replaced. Moreover, the retaining ring assembly should be able to stay substantially parallel to the polishing pad after repeated recycling and replacement. The parallel relationship between the polishing pad and the retaining ring assembly is desirable to eliminate any angular deformities that could result in substandard CMP polishing.
There is a need to for an apparatus and method, which overcomes the foregoing and other problems and which substantially reduces the cost of the retaining ring assembly in a CMP apparatus. It is to these ends that the present invention is directed.